CYTHEROPTERON ALATUM. 35 



Cretaceous and Tertiary. Gijprid'ma monoceros, Reuss, 1855 (narrow) ; Speyer, 



1863 (narrow). 

 Tertiary. Gypridina undulata, Speyer, 1863. Expanded. 

 Recent. Gytheropteron gibbosum, Brady, 1868. Expanded. 

 Recent. — inornatum, Brady and Robertson, 1872. Expanded. 



Recent. — alatum, Sars, 1865; Brady and Robertson, 1872; 



Brady and Norman, 1889. Expanded form. 

 Post-tertiary, Gytheropteron arcuatum, Brady, Crosskey, and Robertson, 1874; 



Brady and Norman, 1889. P]xpanded form. 

 Tertiary. Gytheropteron pipistrella, 'Bra.dj, 1878. ,, ,, 



Recent. — intermedium, Brady, 1878. ,, ,, 



Recent. — crass/spmfti?MH,, Brady and Norman, 1889. Expanded. 



Recent. — hamatum, Brady and Norman, 1889. Expanded. 



Gytheropteron alatum (Bosquet) is one of tlie expanded forms, though not so 

 widely expanded as some ; and we are still inclined to take it as a convenient type 

 for some varieties from the Chalk in our collections, because their differences do not 

 appear to be of specific value. It was from the Ghalh of Maastricht. We have 

 seen a specimen very near to Bosquet's type in Mr. C. D. Sherborn's collection 

 of fossil Ostracoda from a clay at the foot of the cliff at Havre, France. 



3*. Cytheeopteron alatum (Bosquet), var. robusta, nov. (vel alatum-robustum) . 



Plate II, figs. 24—27. 



Cttheeeis alata {Bosquet), Jones. Monogr. Entora. Cret., 1849, p. 21, pi. v, 



figs. 14 fl — d. 



Length "883 ; height "5 ; thickness '61 mm. 



This rather rare form, figured and described in the ' Monograph,' 1849, was 

 referred to the Cythere alata of Bosquet ; but its squarer outline, well-rounded 

 and denticulate front margin, and spinose posterior edge of the wing characterise 

 it as a variety, which we propose to term robusta. 



Prof. Reuss referred a very similar but neater and weaker specimen^ to C. 

 serratula, Bosquet, the outer edge of the wings being slightly tuberculate. 



Localities. — GhalJc, Norwich ; Detritus, Charing. 



1 ' Elbthalgeb.,' &c., 1874, p. 148, pi. xxvii, figs. 8 a, h. 



